1. Field of the Invention
This present invention relates to motor vehicles.
2. Description of the Prior Art
Steel wheels running on steel tracks roll with very little friction to make railroad trains very efficient. Such trains work well for point to point operation between terminals connected by the tracks. However, the steel wheels would work badly on most other road surfaces where abrasive effects would damage the steel wheels, and the hardness of the steel wheels would damage most road surfaces. Rubber tired wheels work well on most road surfaces, but cause significant rolling resistance due to friction.
Being limited to operation on tracks, trains are inefficient in providing door to door service. Our extensive network of roads means that rubber tired vehicles can be very effective in the kind of distributed delivery operations that are usually needed. This is true whether the loads are passengers or freight. Road vehicles can often provide door to door service, or if not, the number of transfers in the course of a journey can be significantly less. Thus road vehicles offer significant advantages over railroad vehicles.
There is a separate congestion problem that arises from having a large number of rode vehicles on the roads, extensive though the network of such roads might be. The well known benefits of mass transit systems are often promoted as a solution. The inescapable fact is however, that even with serious congestion, when time is at stake the transportation choice usually turns out to be in favor of the road vehicle. This is readily supported by observation, where a steady flow of trucks can very often be seen operating on roads that are generally parallel to railroad tracks. Given this reality, it seems reasonable to explore ways to make the more flexible transportation options more workable, whether these be cars to take people door to door or trucks to take freight door to door, or at least for freight to minimize the connections involved in the journey.
Even if aerodynamic drag forces are greatly reduced, we still have the problem of rolling resistance which is present at all speeds. To a first approximation, the energy lost with a given vehicle due to this form of drag is simply proportional to a product of the travel distance and the total load on the wheels. While this rolling resistance is a problem for automobiles, it is a much more serious problem for trucks where their great weight translates into large rolling resistance force due to the rubber tire friction effects.
We have as background a great amount of information about railroad wheel and track systems. Especially relevant is the braking issue, where slipping of steel wheels on steel rails is a long known concern that has generated a large amount of patent literature, largely related to ways to start trains under heavy loads. A rule heard by the present inventor long ago was that if a locomotive wheel slipped on a track, even briefly, that wheel was damaged to the point that it would have to be replaced.
There is also much background available on rubber tires and their construction. As a matter of definition, a tire here refers to any material on the perimeter of a wheel that deforms under load to conform to a road surface.
Furthermore, anti-lock brake mechanisms are also extensively developed for use where wheels are equipped with such tires.
There is also much knowledge of hydroplaning effects for tires on roads. It is relevant also for steel wheels, but the size of the contact spot being small for steel wheels on rails, pressure being thus high, the hydroplaning effect is said to be minimized.
We also have body of data on coefficient of friction between various materials, including various road surfaces relative to rubber and various metals, including steel on steel. Other choices of metals are not beyond consideration in looking for the best possible wheel arrangements. In general, steel is the most common form of rigid wheel; that being the wheel use by railroad equipment.
In existence are arrangements whereby road vehicles with rubber tires are also fitted with steel wheels to enable those road vehicles to run on railroad tracks. These are known to be used in railroad service vehicles, where apparently the rubber tires in contact with the steel rails provide the driving and braking force, while the steel wheels maintain the service vehicle in position on the steel rails as a result of a flange on the steel wheels. A mechanism is involved in lowering and raising the steel wheels according to the service needed, thus, the steel wheels can be withdrawn so as to be not involved in operation on general road surfaces.
Further background of relevance is the apparatus used to raise and lower extra wheels on trucks that carry heavy loads, particularly ready-mix concrete trucks and dump trucks. These use hydraulic means to control force on such extra wheels as well as to raise and lower them when needed.